A subsidiary title is an hereditary title

Hereditary Title

Hereditary titles, in a general sense, are titles, positions or styles that are hereditary and thus tend or are bound to remain in particular families....

 held by a royal

Royal family

A royal family is the extended family of a king or queen regnant. The term imperial family appropriately describes the extended family of an emperor or empress, while the terms "ducal family", "grand ducal family" or "princely family" are more appropriate to describe the relatives of a reigning...

 or a noble

Nobility

Nobility is a social class which possesses more acknowledged privileges or eminence than members of most other classes in a society, membership therein typically being hereditary. The privileges associated with nobility may constitute substantial advantages over or relative to non-nobles, or may be...

 but which is not regularly used to identify that person.

For example, the Duke of Norfolk

Duke of Norfolk

The Duke of Norfolk is the premier duke in the peerage of England, and also, as Earl of Arundel, the premier earl. The Duke of Norfolk is, moreover, the Earl Marshal and hereditary Marshal of England. The seat of the Duke of Norfolk is Arundel Castle in Sussex, although the title refers to the...

 is also the Earl of Arundel

Earl of Arundel

The title Earl of Arundel is the oldest extant Earldom and perhaps the oldest extant title in the Peerage of England. It is currently held by the Duke of Norfolk, and is used by his heir apparent as a courtesy title. It was created in 1138 for the Norman baron Sir William d'Aubigny...

, the Earl of Surrey

Earl of Surrey

The Earl of Surrey is a title in the Peerage of England, and has been created five times. It was first created for William de Warenne, a close companion of William the Conqueror...

, the Earl of Norfolk

Earl of Norfolk

Earl of Norfolk is a title which has been created several times in the Peerage of England. Created in 1070, the first major dynasty to hold the title was the 12th and 13th century Bigod family, and it then was later held by the Mowbrays, who were also made Dukes of Norfolk...

, the Baron Beaumont

Baron Beaumont

The title of Baron Beaumont is an ancient one in the Peerage of England, created in 1309 for a younger part of the de Brienne-family. The sixth Baron Beaumont was created Viscount Beaumont in 1432; after the death of the 2nd Viscount both titles fell into abeyance...

, the Baron Maltravers

Baron Maltravers

The title Baron Mautravers or Baron Maltravers was created in the Peerage of England on 25 January 1330, by writ of summons, for John Mautravers or Maltravers. It went into abeyance on his death in 1364; this was terminated by the death of his granddaughter Joan Mautravers without issue c. 1383,...

, the Baron FitzAlan, the Baron Clun, the Baron Oswaldestre, and the Baron Howard of Glossop

Baron Howard of Glossop

Baron Howard of Glossop, in the County of Derby, is a title in the Peerage of the United Kingdom, since 1975 a subsidiary title of the dukedom of Norfolk. It was created in 1869 for the Liberal politician Lord Edward Howard, the second son of Henry Fitzalan-Howard, 13th Duke of Norfolk...

. In day-to-day practice, the individual who holds all of these titles would be referred to only by his most senior title - in this case, "Duke of Norfolk" - while all of his other titles would be subsidiary titles.

In the United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, a noble's heir apparent

Heir apparent

An heir apparent or heiress apparent is a person who is first in line of succession and cannot be displaced from inheriting, except by a change in the rules of succession....

 may use his parent's most senior subsidiary title as a courtesy title

Courtesy title

A courtesy title is a form of address in systems of nobility used for children, former wives and other close relatives of a peer. These styles are used 'by courtesy' in the sense that the relatives do not themselves hold substantive titles...

, provided that it causes no confusion. For example, the Duke of Norfolk's heir apparent is known as "Earl of Arundel", although the son does not technically become Earl of Arundel until his father's death and is legally still a commoner

Commoner

In British law, a commoner is someone who is neither the Sovereign nor a peer. Therefore, any member of the Royal Family who is not a peer, such as Prince Harry of Wales or Anne, Princess Royal, is a commoner, as is any member of a peer's family, including someone who holds only a courtesy title,...

.

If a subsidiary peerage has the same name as a higher peerage, it is not used as a courtesy title. For example, the Duke of Manchester

Duke of Manchester

Duke of Manchester is a title in the Peerage of Great Britain. It was created in 1719 for the politician Charles Montagu, 4th Earl of Manchester, who notably served as Secretary of State for the Southern Department. The Duke of Manchester is styled His Grace.-Origin and descent:The Montagu family...

 is also Earl of Manchester, but his heir is styled "Viscount Mandeville".

An heir apparent can be summoned to the House of Lords

House of Lords

The House of Lords is the upper house of the Parliament of the United Kingdom. Like the House of Commons, it meets in the Palace of Westminster....

, before his parent's death, by a writ of acceleration

Writ of acceleration

A writ in acceleration, commonly called a writ of acceleration, was a type of writ of summons to the British House of Lords that enabled the eldest son and heir apparent of a peer with multiple peerage titles to attend the British House of Lords or Irish House of Lords, using one of his father's...

 – that is, by accelerating the inheritance of a junior title (usually a barony). For example, a writ of acceleration could cause a courtesy Earl of Arundel to inherit the Maltravers barony prematurely, whereupon he would join the House of Lords as Lord Maltravers.